Buffering up in Tcl - the empty coke can comparison

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A comment on buffering in Tcl ....

if {1 == 0} {

When you finish drinking a can of Coke, you don't call

your local recycling plant up straight away and have them

send a truck around to collect the empty - that would be

inefficient to put it mildly.   And in the same way, 

a computer doesn't always save its output character by 

character to the disc or screen - rather it buffers it up.

In most languages a clever strategy controls when the buffer

really is written (flushed) so that it's not very common for

the programmer to have to add an explicit flush request.

 

With Tcl, the default is that the output buffer flushes

each time it receives a new line character, which works

well enough most of the time.  However, there are occasions

that you'll want to use the -nonewline option to puts to

allow you to generate a prompt and leave the cursor hanging

on the same line awaiting input from the user, and in such

cases you'll need an extra flush command.

}

 

puts -nonewline "How old are you "

flush stdout

set age [gets stdin]

puts "You are $age years old then"

 

if {1 == 0} {

Where you have multiple user inputs, you may prefer to

use a proc to read inputs and encapsulate the flush within

it, or you may prefer to run

 

fconfigure stdout -buffering none

 

which (technically) turns autoflush mode on rather than 

turning buffering off!

}

If you want to comment a whole block of code .... you might like to use my little trick of testing for the impossible - "1 == 0" in the above - which lets you put code aside neatly, cleanly and nested. You'll see that I've even used it to provide documentation for today's entry ...
(written 2007-11-10 06:33:13)

Associated topics are indexed under

T202 - Tcl/Tk - Tcl Fundamentals
T209 - Tcl/Tk - File and Directory Handling

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